Strain engineering in monolayer WS2and WS2nanocomposites

There has been a massive growth in the study of transition metal dichalcogenides (TMDs) over the past decade, based upon their interesting and unusual electronic, optical and mechanical properties, such as tuneable and strain-dependent bandgaps. Tungsten disulphide (WS2), as a typical example of TMDs, has considerable potential in applications such as strain engineered devices and the next generation multifunctional polymer nanocomposites. However, controlling the strain, or more practically, monitoring the strain in WS(2)and the associated micromechanics have not been so well studied. Both photoluminescence (PL) spectroscopy and Raman spectroscopy have been proved to be effective but PL cannot be employed to characterise multilayer TMDs while it is difficult for Raman spectroscopy to reveal the band structure. In this present study, PL and Raman spectroscopy have been combined to monitor the strain distribution and stress transfer of monolayer WS(2)on a flexible polymer substrate and in polymer nanocomposites. It is demonstrated that WS(2)still follows continuum mechanics on the microscale and that strain generates a non-uniform bandgap distribution even in a single WS(2)flake through a simple strain engineering. It is shown that these flakes could be useful in optoelectronic applications as they become micron-sized PL emitters with a band gap that can be tuned by the application of external strain to the substrate. The analysis of strain distributions using Raman spectroscopy is further extended to thin-film few-layer WS(2)polymer nanocomposites where it is demonstrated that the stress can be transferred effectively to WS(2)flakes. The relationship between the mechanical behaviour of single monolayer WS(2)flakes and that of few-layer flakes in bulk composites is investigated.